Catalyst compositions formed by transition metal cations and methods of making and using such catalysts

ABSTRACT

Catalyst compositions containing the cations M22 , M2(OCOR)4 nn , M2(OCSR)4 nn , M2(OCSR)4 n WHERE M is a transition metal which are useful for hydrogenation, hydroformylation, carbonylation, isomerization, disproportionation, and hydrosilation reactions, and methods of making by protonation of corresponding carboxylates, thiocarboxylates, or dithiocarboxylates.

United States Patent 1191 Wilkinson [54] CATALYST COMPOSITIONS FORMED BYTRANSITION METAL CATIONS AND METHODS OF MAKING AND [2]] Appl. No.:53,031

[30] Foreign Application Priority Data July 14, 1969 Great Britain..35,249/69 [52] US. Cl. ..252/429 R, 252/428, 252/431 C [51] Int. Cl..C07 5/02 58 Field ofSearch ..252/'431'C, 4311i; 4311 11 3,725,305 [4 1Apr. 3, 1973 [56] I References Cited UNITED STATES PATENTS 3,511,3855/1970 Hughes .252/431 C X 3,542,751 11/1970 Throckmorton... ....252/431c X 3,558,517 1/1971 l-lugheset al. ...252/431 C x 3,574,734 4/1971 Bond..252/431 C x PrimaryExaminer-Patrick P. Garvin Attorney-Cushman, Darby& Cushman [s7 ABSTRACT 20 Claims, No Drawings CATALYST COMPOSITIONSFORMED BY TRANSITION METAL CATIONS AND METHODS OF MAKING AND USING SUCHCATALYSTS In this case the cationic species with one positive Thisinvention relates to new catalyst compositions charge also Shows goodcatalytlc activity formed by transition metal cations, to methods ofmaking such catalysts and to reactions whichmay be per formed usingthese compositionsas catalysts.

We have found that certain novel compositions containing the cations:

A M-n" A XM (where M is a transition metal) are useful as catalysts fora variety of chemical reactions.

In the above:

n is a positive integer from 1 to 4. Where n=4 the cation M is presentalone and isan efiective catalyst;

(OCOR) represents a carboxylate radical;

(OCSR) represents a thiocarboxylate radical; and

(SCSR) represents a dithiocarboxylate radical.

According to one aspect of t the invention :there is provided a catalystcomposition including any of the cations:

M,(OCSR or M (SCSR) where M, (OCOR),

(SCSR) and n are defined above.

According to another aspect of the invention a method of making such acomposition comprises protonating with a strong acid a solution.ofcarboxylate, a thiocarboxylate or a dithiocarboxylate having thegeneral formulas:

M,(SCSR),L, where R is a substituted or unsubstituted aryl or alkylgroup and L is an anionic or neutral ligand;

M is preferably either a platinum group metal or Mo, Cr, Cu, or Re, andpreferred platinum group metals are Rh, Ru and Ir;

R may for example be C,H C l-l cc1,, CF CH,Cl, CH CH 'C H C l-lnaphthyl, or a substituted phenyl, and

L may for example be H O, C H OH, CO, pyridine Cl, or Br.

The cationic species produced are generally, but not necessarilybinuclear. When the oxidation state of the metal is formally II abinuclear metallic cation may have a charge of +4. in one example, thereaction proceeds as follows:

(OCSR),

Partial displacement of the carboxylate or substituted carboxylate,instead of full displacement may take place; for example:

Some examples of the catalyst precursor compounds which produce activespecies according to this invention on protonation are:

Especially effective are the tetracetate compounds, i.e. those of thefirst column, when R CH Oxidationstates other than 2 can be involved.For example the ruthenium complex Ru (OCOR),Cl contains formally Ru(II)and Ru(lII) (see example 3 below). The rhenium complex Re (OCOR),Clcontains formally, Re(IlI).

The strong acid referred to above may for example be'fluoroboricacid,perchloric acid, fluorosulphuric acid, tri-fluoremethane sulphuric acid,sulphuric acid or hydrofluoric acid; hydrofluoric acid may be used aloneor in combination with a Lewis acid such as SbF Sif, or BF According toa preferred feature of the invention there is provided a catalystcomposition containing the species:

z z( )4-n" For the purpose of brevity and clarity, additional neutral ornegative ligands indicated above, suchas H O, are not always indicatedas being present in cationic species in this specification. This wouldnot, of

course, be taken to mean that such species are definitely excluded.

. The cationic species may be absorbed onto cation exchange resins orsimilar exchange solids such as zeolites, phosphates (e.g. Calgon) etc.They may also be adsorbed onto activated charcoal and other similarsolids.

The solid material is preferably a cation exchange resin such assulphonated polystyrene in the form of porous resin beads.

According to further features of the invention, we also provide methodsof carrying out chemical reactions using compositions containing thecationic species indicated as catalysts.

If the cationic species liberated by protonation is adsorbed on to acation exchange resin (or a similar exchange material as describedabove), the resulting material is useful for example as a heterogeneouscatalyst for hydrogenation, carbonylation, hydroformylation and therelated reactions of olefine or other organic materials either in thegas or liquid phase, or in suspension solution (with beads ofion-exchange resin, for example.) Ambient or elevated temperatures maybe used. 1 I

Such solid state catalysts will also promote for examle: p a. thecarbonylation of methanol to acetic acid,

b. the carbonylation of amines toamides,

c. the isomerization and disproportionation of alkenes, alkapolyenes andrelated compounds, and

d. the hydrosilation of alkenes.

Solutions of the metal carboxylate, thio or dithiocarboxylate inmethanol (or a similarly polar solvent) in the presence of excessprotonating acid (e.g. HEP and subsequent addition of additional donorligand for stabilization purposes are active catalysts for example forthe hydrogenation of alkenes of all types including conjugated polyenes,acetylanes generally (R'C CR where R and R may also be H) and otherunsaturated substrates containing carbon carbon double and triple bondssuch as carboxylic acids, ketones, ethers, steroids, esters andalcohols, for example at 25C and atmospheric pressure.

Some suitable donor ligands for stabilization purposes are:

R R R sb R,R R N in which R,, R and R may be the same or different andmay be hydrogen, aryl or alkyl substituents. Heterocyclic N-bases suchas pyridine, dipyridyl, etc., are also suitable donor ligands.

Generally speaking, suitable donor ligands for stabilization purposesare either:

a. an organic isocyanide,

b. an organic compound having in the molecule an atom of an elementselected from groups 5B or 6B of the Periodic Table, that is, usually aN, P, As, Sb, 0, S or Se atom, such atom being in such a valency statethat it possesses a lone pair of electrons; or

c. a stannous of germanium (II) halide.

Preferred ligands within the definition of categories (a) and (b)include: tertiary amines, phosphines, arsines and stibines; organicnitriles and isocyanides; sulphoxides, phosphine oxides, dialkylsulphides and mercaptans.

For example, there may be employed pyridine, quinoline ordimethylaniline; though less basic compounds are preferred, for example;tributyl or triphenyl phosphine, dimethylphenylarsine, triphenyl arsineor stibine, dibutyl sulphide, dimethyl sulphoxide, triphenyl phosphineoxide, phenyl isocyanide or acetonitrile. Also to be treated as organiccompounds for present purposes are ligands within category (b) such asphosphorus tri-isocyanate and phosphorus tri-isothio cyanate.

Such donor ligands for stabilization purposes are often described asbiphyllic ligands. By biphyllic ligand" is meant a compound having anelement with a pair of electrons capable of forming a co-ordinate bondwith a metal atom and simultaneously having the ability to acceptelectrons from the metal, thereby providing additional stability to theresulting complex. The term biphyllic ligand has been defined by R. G.Pearson see J.A.C.S. 82 787 (1960). The carbon monoxide molecule is anexample of a suitable biphyllic ligand.

The biphyllic ligand may also be a polydentate compound, co-ordinatingat more than one position to the central metal atom or ion.

Catalysts according to this invention have an advantage over other homogen eous catalysts such as RhCl(PPh RhH(CO)PPh or RuH(Cl) (P Ph in thatthey are completely and readily soluble in polar solvents such asmethanol, olefinic substrates to be hydrogenated which are insoluble orsparingly soluble or benzene-alcohol mixtures can now be hydrogenated ina wholly polar medium.

Catalyst solutions according to this invention will also catalyze thehydroformulation reactions of alkenes, alkynes and other unsaturatedmaterials with C=C and C E C bonds. These reactions may be carried outusing carbon monoxide and hydrogen mixtures (which can be 1:1 or otherratios) at temperatures from 15C 200C or above, and at pressures from 1atm upwards.

Catalyst solutions according to this invention will also isomerizealkenes and other unsaturated substances by causing double bondmigration as well as cis trans isomerization.

Solutions according to this invention will catalyze the formation ofacetic acid from methanol and carbon monoxide under mild conditions(e.g. C and under 50 atm. pressure). In this case the presence of ahalogen promoter is desirable and methyl iodide has been found to be asatisfactory one in this case.

The foregoing are only some of the chemical reactions for which thecompositions according to the invention can act as catalysts.

The invention will now be described in more detail with reference to thefollowing examples.

EXAMPLE 1 Commercial rhodium trichloride trihydrate (5.0 g) I and sodiumacetate trihydrate (10.0 g) in glacial acetic acid (100ml) and absoluteethanol (100 ml) were gently refluxed under nitrogen for an hour.

The initial red solution rapidly became green and a green solid wasdeposited. After cooling to room temperature the green solid wascollected by filtration through a Buchner or sintered filter funnel.

The crude product was dissolved in boiling methanol (ca.600 ml) andfiltered; after concentration to about 400 ml the solution 'was kept ina refrigerator overnight. After collection of the crystals, the solutionwas concentrated and cooled to yield a further small amount of themethanol adduct [Rh(OCOCI-I;,),],.2CH 01-1.

The blue green adduct was heated in vacuum at 45 for 20 hours to yieldemerald green crystals of [Rh(OC OCI-l A check on the removal ofmethanol was made periodically by taking an infrared spectrum.Properties The copper acetate type structure has been shown by X-raydiffraction. The complex is diamagnetic; it is only slightly soluble inwater, methanol, acetone, etc., giving green solutions. Adducts with avariety of ligands have been characterized.

The infrared spectrum has bands at 1580s, 1425s, 1355m in nujol mulls(in hexachlorobutadiene 1445s, 1415s, l350m) due to carboxylatefrequencies, as well as CH absorption.

The addition of a stoichiometric amount of aqueous concentratedfluoroboric acid to a methanol or water suspension of the acetate of 60gives a clear green solution after about 12 hours whichcontains the ionRh The green solution of Rh," in methanol normally requires the presenceof other stabilizing donor ligands, as described above in order toexhibit any substantial catalytic activity.

On the addition of a stabilizing donor ligand such as triphenylphosphine, for example, to the green solution an active catalyst for thehomgeneous hydrogenation of alkenes and alkynes is obtained. Comparativerates of reaction under standard conditions are given in Example 2.

The catalyst solution in the following examples was made up as requiredfrom a stock solution of Rhf in methanol and the phosphine was added,via a syringe, to the reaction flask. The apparatus and generaltechniques used have been described previously in J. Chem. Soc. (A) 1966p.1711.

Catalytic activity of the protonated solution is highest with a Rh P Phratio of 1:2. The activity appears to be poisoned by oxygen andcarbonmonoxide, and this effect cannot be reversed by sweeping withhydrogen.

The solutions with Rh:P Ph of 1:2 are normally red, but on addition ofcertain unsaturated substances, notably unsaturated carboxylic acids andalcohols, a change in color to yellow-green occurs, presumably due tothe formation of complexes, possibly of Rh (II).

The methanolic solutions of Rh react with many donor ligands, e.g. R NCSamines,.etc., to give a wide variety of complexes. With oxygen donorssuch as dimethyl sulphoxide, hexamethyl phosphoramide, alcohols, ketonesand esters, the solutions stay green and presumably these substances aremerely solvating the 1011.

Where the preparation of a carboxylate compound complex or ionic speciesis described in this specification, the corresponding thioanddithio-analogues may be assumed to be prepared similarly, withappropriate modifications.

EXAMPLE 2 Rhodium system The activity of protonated Rh solution preparedas in Example 1 for the hydrogenation of various substrates is givenbelow:

( [Rh]== 2.50 mM, [acetylene or olefin]= 1.0 M, P 45 cm, solventmethanol, Reaction temperature 25, [PPh 5.0mM)

Substrate Rate ml/min Substrate Rate ml/min. Hex-l-ene i0.9 nJ-lexJ-yne34.2 cis and trans 3.3 3 methyl butyn Hex-Z-ene l-ol-3 44.8 cisHept-Z-ene 2.2 Propargyl alcohol 17.6 Cyclohexene l .1 Acetylenedicarboxylic acid 0.l 1.5 Hexadiene 36.6 allylphenyl 14.1 Cyclo octaether LS-diene 0.6" Diethyl maleate 4.8 Maleic acid 0.2 (a) [PPhfl 20.0mM

b H 50 mm EXAMPLE 3 Ruthenium system The activity of protonated Ru000C11 Cl for the hydrogenation of various substrates is given below:

( [Ru] 2.50 mM, [acetylene or olefin]= 1.0M, P

= cm, solvent methanol; Reaction temperature 25, [PPh 5.0 mM) Theactivity of a ruthenium catalyst made by the protonation of Ru (OCOMe).2PlPh under hydrogen is given below:

( [Ru] 2.50 mM, [acetylene or olefin] 1.0M, PH2

' 45 cm, reaction temperature 30C, PPh 5.0

mM, solvent methanol Substrate Rate ml/min Hex-l-yne 0.4

Hex- 1 -ene 41.8

Cyclo octa 1,5 diene 48.7

(a) P mm Ruthenium acetate and its adducts with triphenyl phosphine andpyridine may be prepared as described in Example 10.

EXAMPLE 4 V Molybdenum system EXAMPLE 5 Hydroformylation Solutions withRh:PPh of 1:2 were found to be active for hydroformylation reactions.

Rh,(OCOCH 4HBF 4PPh in methanol (corresponding to 5 mM metalconcentration) containing substrate hex-l-ene (1M) was treated with C0H, (1:1) at 35C and either 45 cm or 1 atm pressure. After 15 hours theformation of heptaldehydes was confirmed by g.l.c. The rate wasincreased at higher pressures and temperatures.

EXAMPLE 6 Acetic Acid synthesis 1 A 1:2 ratio of Rh:PPh is alsoeffective for the carbonylation of methanol to acetic acid and methylacetate,

Rh,(OCOCH;,) ti-[13F 4PPh, in methanol (ca. 2.5 mM metal concentration)was treated with CO at /50 atm. pressure in presence of a trace ofmethyl iodide. The formation of acetic acid was detected by g.l.c. Using5 ml of a 0.02 M Rh, solution and 45 mls methanol the reaction occurredat 100C and 25 atm CO.

EXAMPLE 7 Heterogeneous Catalysis (a) A 2 g sample of Dowex (aregistered trade mark of the Dow Chemical Company) 50W-X8 cationexchange resin (20-50 MS mesh H form) was allowed to absorbed theprotonated aqueous fluroboric acid (2M) solution of rhodium (II) acetate(0.1 g). The now green resin was washed with methanol and then treatedwith a methanol solution saturated with triphenyl-phosphine which turnedthe resin red. The resin catalyst thus prepared was suspended inmethanol (50 ml) and hex-l-ene (6 ml, 1M) was added. At 50 cm hydrogenpressure the rate of uptake at 20C was found to be ml. min.

(b) ml of resin, prepared as in (a), holding Rh equivalent to a 10 mMsolution at P 45 cm, [PPh SmM, reaction temperature C, gave a rate for lM hex-l-ene of l mLmin".

EXAMPLE 8 The benzoate complex itself may be obtained in a mannersimilar to that of the acetate, i.e. with benzoic acid and sodiumbenzoate instead of acetate acid and sodium acetate.

Bis (triphenyl phosphine) and his (pyridine) adducts may also beobtained with the benzoate complex.

EXAMPLE 9 The table below gives data for the hydrogenation of hex-l-eneobtained at C using the Rh 4 /PPh catalyst under a range of catalyticconditions. These results indicate the dependence of the rate ofhydrogenation as a functionof [Rh], [hex-l-ene], and H pressure (PAlthough at the lower concentrations of rhodium, hexene and H theobserved rates show approximately first order dependence on each ofthese concentration variables, the rate dependencies deviate markedlyfrom linearity at the higher concentrations. This would seem to suggestthat a number of complex equilibria may be involved. As noted earlier,the ratio of Rh:PPh of 1:2 is the most favorable and was usedthroughout. Rates of hydrogenation of hex-l-ene at 30C using the Rh PPh,catalyst under a range of conditions.

[Rh] P Hex-l-ene] [PPh,] Rate X 10 mM mm M mM M.sec."

EXAMPLE l0 Protonation of Ru,( OCOMe ),Cl and Ru, (OCOMe Lli Thechloroacetate is readily protonated by fluoroboric acid in methanol at60C under conditions similar to those used for rhodium (ll) acetate. Thefinal solution is deep blue and extremely air sensitive, turning firstgreen on exposure to air and finally yellowbrown. The blue solution isreadily absorbed onto a cation exchange resin (H form) and the eluatecan be shown to contain acetic acid, as in the rhodium case. Theelectronic absorption spectrum of the aqueous protonated solution. Amax(E) 437 (460), 537 sh is different from that of the aqueous solution ofRu (OCOMe) Cl, 423 (750). The exact nature of the cationic species isnot certain at present.

Although the blue'solutions are not catalytically active under mildconditions, again like the rhodium system, the addition of a stabilizingdonor or biphyllic ligand such as triphenyl phosphine immediately givesa very active catalyst for the hydrogenation of alkenes and alkynes (seeExample 3) without causing any initial 'color change. Under hydrogen theblue solution becomes a more greenish blue and, as the hydrogenation ofalkene proceeds, the solution becomes mauve.

The protonated adduct Ru (OCOMe) .2PPh in the presence of excesstriphenyl phosphine produced a catalytic species that catalyzed thehydrogenation of hex-l-ene. (See example 3A).

Green ruthenium -(II) acetate, Ru,(OCOMe) is obtained by the interactionof commercial ruthenium trichloride with acetic acid, sodium acetate andethanol under reflux. It is difficult to obtain the acetate entirelyfree of sodium acetate and solvent, but it can be readily isolated asits green triphenyl phosphine adduct Ru (OCOMe) PP,h The acetate and itsadduct are both diamagnetic (n.m.r.). The bis(pyridine) adducts issimilarly isolatable as dark blue crystals.

No hydrogenation was observed when using the protonated adduct in excesstriphenyl phosphine for cis-pent-2-ene and other internal alkenes suchas cyclohexene. From this point of view the ruthenium catalyst appearedto be much more selective than the corresponding rhodium phosphinecatalyst.

Selectively was also observed between cyclic nonconjugated dienes, cycloocta 1,5 diene being hydrogenated very rapidly in contrast to a muchslower rate for bicyclo (2.2.1) hepta-2,5 diene.

What is claimed is:

l. A catalyst solution containing a catalytically effective amount of acation selected from the group consisting of:

A L-H A L-J the said solution being prepared by the addition of strongacid to a solution of a compound selected from the group consisting of M(OCOR M,(OCOR).L

M,(SCSR),L and where M is a metal selected from the group consistingofMo, Cr, Cu, Re and metals of the platinum group;

R is selected from the group consisting of alkyl and aryl;

L is a ligand selected from the group consisting of H 0, CH Ol-l, C HOH, CO, pyridine, Cl" and Br;

n is a positive integer from 1 to 4;

(OCOR) represents a carboxylate radical;

(OCSR) represents a thiocarboxylate radical, and

(SCSR) represents a dithiocarboxylate radical, and

the said solution including a stabilizing amount of a donor ligandselected from the group consisting of pyridine, quinoline,dimethylaniline, tributylphos phine, triphenylphosphine,dimethylphenylarsine, triphenylarsine, triphenylstibine, dibutylsulphide, dimethyl sulphoxide, triphenylphosphine oxide, phenylisocyanide, acetonitrile, phosphorus tri-isocyanate, phosphorustri-isothiocyanate, stannous halide and germanium (II) halide.

2. A catalyst solution according to claim 1 in which the metal of theplatinum group is selected from the group consisting of rhodium andruthenium.

3. A catalyst solution according to claim 2 in which a platinum groupmetal and triphenylphosphine are present in the approximate ratio of1:2.

4. A catalyst solution according to claim 1 in which the strong acid isselected from the group consisting of fluoroboric acid, perchloric acid,fluorosulphuric acid, trifluoromethane sulphuric acid, sulphuric acid,hydrofluoric acid and hydrofluoric acid in combination with a Lewisacid.

5. A catalyst solution according to claim 4 in which the Lewis acid isselected from the group consisting of a SbF,,, SiF and BF,.

6. A catalyst solution according to claim 1 in which R is selected fromthe group consisting of C,H C l-l CCl CF CH Cl, CH CH -C H and napthyl.-

7. A catalyst solution according to claim 1 in which M,(OCOR) isselected from the group consisting of MO2(OCOCH3)4 Cu,(OCOCH 8. Acatalyst solution according to claim 1 in which M,(OCR) is Ru,(OCOCH Cl.

9. A catalyst solution according to claim lin which M,(OCOR)L, isselected from the group consisting of 10. A catalyst solution accordingto claim 1 in which M,(OCSR) is selected from the group consisting ofMo,(OCSCH Re OCSCl-I and 11. A catalyst solution according to claim 1 inwhich MAOCSR) is Ru (OCSCH ),Cl.

12. A catalyst solution according to claim 1 in which M (OCSR)L isselected from the group consisting of R OCSCI-l c1 and n ilocscuiifi do13. A catalyst solution according to claim 1 in which M (SCSR), isselected from the group consisting of Cr,(SCSCH Re,(SCSCH 14. A catalystsolution according to claim 1 in which M (SCSR) is Ru,(SCSCH Cl.

15. A catalyst solution according to claim 1 in which M (SCSR) C2 isselected from the group consisting of Re2(SCSR) Cl2 and 16. A catalystcomposition consisting essentially of a cation exchange solid havingexchanged on to it a cation selected from the group consisting of A LJby passage through it of a solution according to claim 1.

17. A catalyst composition according to claim 16 in which the cationexchange solid is selected from the group consisting of cation exchangeresins, zeolites and phosphates.

18. A' catalyst composition according to claim 17 in which the cationexchange resin is in the form of porous sulphonated polystyrene resinbeads.

19. A catalyst composition according to claim 1 when adsorbed on toactivated charcoal.

2. A catalyst solution according to claim 1 in which the metal of theplatinum group is selected from the group consisting of rhodium andruthenium.
 3. A catalyst solution according to claim 2 in which aplatinum group metal and triphenylphosphine are present in theapproximate ratio of 1:2.
 4. A catalyst solution according to claim 1 inwhich the strong acid is selected from the group consisting offluoroboric acid, perchloric acid, fluorosulphuric acid,trifluoromethane sulphuric acid, sulphuric acid, hydrofluoric acid andhydrofluoric acid in combination with a Lewis acid.
 5. A catalystsolution according to claim 4 in which the Lewis acid is selected fromthe group consisting of a SbF5, SiF4 and BF3.
 6. A catalyst solutionaccording to claim 1 in which R is selected from the group consisting ofC2H5, C3H7, CCl3, CF3, CH2Cl, CH3, CH3.C6H5 and napthyl.
 7. A catalystsolution according to claim 1 in which M2(OCOR)4 is selected from thegroup consisting of Rh2(OCOCH3)4 Mo2(OCOCH3)4 Cr2(OCOCH3)4 Ru2(OCOCH3)4Cu2(OCOCH3)4 Re2(OCOCH3)4 and Ir2(OCOCH3)4.
 8. A catalyst solutionaccording to claim 1 in which M2(OCOR)4L is Ru2(OCOCH3)4Cl.
 9. Acatalyst solution according to claim 1 in which M2(OCOR)L2 is selectedfrom the group consisting of Re2(OCOCH3)4Cl2 and Re2(OCOCH3)4(CO)2. 10.A catalyst solution according to claim 1 in which M2(OCSR)4 is selectedfrom the group consisting of Rh2(OCSCH3)4 Mo2(OCSCH3)4 Cr2(OCSCH3)4Ru2(OCSCH3)4 Cu2(OCSCH3)4 Re2(OCSCH3)4 and Ir2(OCSCH3)4.
 11. A catalystsolution according to claim 1 in which M2(OCSR)4L is Ru2(OCSCH3)4Cl. 12.A catalyst solution according to claim 1 in which M2(OCSR)L2 is selectedfrom the group consisting of Re2(OCSCH3)4Cl2 and Re2(OCSCH3)4(CO)2. 13.A catalyst solution according to claim 1 in which M2(SCSR)4 is selectedfrom the group consisting of Rh2(SCSCH3)4 Mo2(SCSCH3)4 Cr2(SCSCH3)4Ru2(SCSCH3)4 Cu2(SCSCH3)4 Re2(SCSCH3)4 Ir2(SCSCH3)4.
 14. A catalystsolution according to claim 1 in which M2(SCSR)4L is Ru2(SCSCH3)4Cl. 15.A catalyst solution according to claim 1 in which M2(SCSR)4L2 isselected from the group consisting of Re2(SCSR)4Cl2 and Re2(SCSR)4(CO)2.16. A catalyst composition consisting essentially of a cation exchangesolid having exchanged on to it a cation selected from the groupconsisting of M2n M2(OCOR)4 nn M2(OCSR)4 nn and M2(SCSR)4 nn by passagethrough it of a solution according to claim
 1. 17. A catalystcomposition according to claim 16 in which the cation exchange solid isselected from the group consisting of cation exchange resins, zeolitesand phosphates.
 18. A catalyst composition according to claim 17 inwhich the cation exchange rEsin is in the form of porous sulphonatedpolystyrene resin beads.
 19. A catalyst composition according to claim 1when adsorbed on to activated charcoal.
 20. A catalyst compositionaccording to claim 1 prepared by the protonation of any of thefollowing: Rh2(OCOMe)4, Rh2(OCOMe)4,2PPh3, Rh2(OCOMe)4.(C5H5N)2,Rh2(OCOPh)4, Rh2(OCOPh)4.2PPh3, Rh2(OCOPh)4.(C5H5N)2, Ru2(OCOMe)4,Ru2(OCOMe)4Cl, Ru2(OCOMe)4Cl2, Ru2(OCOMe)4.2PPh3, Ru2(OCOMe)4.(C5H5N)2,Ru2(OCOPh)4, Ru2(OCOPh)4.2PPh3 or Ru2(OCOPh)4 (C5H5N)2.